The present invention relates to an electron radiation curing type adhesive, and to a polyester film laminated metal plate for cans, using this adhesive.
Heretofore, a polyester film laminated metal plate (which will be hereinbelow denoted as "PET laminated metal plate") used for cans to hold beverages or foods is usually manufactured by laminating a metal plate or cover with a polyester film through the intermediary of an adhesive (as disclosed in, for example, Japanese Laid-Open Patent No. 3-87249).
A conventional method of manufacturing a PET laminated metal plate comprises the steps of: (1) applying an adhesive to a polyester film (which will be hereinbelow denoted as "PET film"), and drying the same until it becomes tack-free (usually at about 50 to 150 deg. C. for several seconds); (2) heating the PET film applied with the adhesive and the metal plate (usually at about 180 deg. C., for 0.5 sec) so as to laminate them together; and (3) after-baking the adhesive (usually at about 180 deg. C. for 60 to 100 sec) which is therefore completely cured.
The above-mentioned conventional manufacturing method has raised the following problems:
(1) an after-baking furnace has to be relatively long in order to satisfy conditions for producing a PET laminated metal plate in a short time through high speed production lines which have become recently required; PA1 (2) in the conventional manufacturing method, insufficiently bonded parts (insufficiently cured parts) are found in the case of laminating speeds of higher than 150 m/min or in the case of temperatures of less than 180 deg. C., that is, unevenness occurs in the external appearance of the product; and PA1 (3) cans for beverages or foods made of a PET laminated metal plate manufactured by conventional methods are inferior in processability (for necking, flanging, beading or the like), whitening or blistering occurs on a parting line which is formed along the barrel of a can in the vicinity of the weld, being caused by welding heat or by baking a side seam paint (at maximum ultimate temperatures of 230 to 240 deg. C. at 90 sec or 240 to 280 deg. C. at 7 to 20 sec) after a retort process, a water spot-like pattern is found on the surface of the PET film, or the surface finish such as luster deteriorates.